Although the red-legged partridge is one of the game bird species most frequently raised in outdoor operations, no studies had previously investigated the infection dynamics of avian influenza viruses in this species. In order to elucidate their putative role in the ecology of influenza A viruses, we evaluated the susceptibility of red-legged partridges to an infection with a HPAIV H7N1 strain (A/Chicken/Italy/5093/1999) and a LPAIV H7N9 strain (A/Anas crecca/Spain/1460/2008) by studying pathogenesis, transmission and viral shedding.
The high pathogenicity of this H7N1 HPAIV strain, evidenced by 100% mortality in this study, is in accordance with standardised IVPI tests for influenza viruses , and in agreement with those obtained in natural H7N1 HPAIV infections in chickens . The only experimental infection published so far with HPAIV in partridges used an H5N1 HPAIV strain as inoculum . In this experiment, 75% of mortality was observed in Chukar partridges (Alectoris Chukar) and MDT was shorter than in our experiment (4.5 dpi). Therefore, mortality due to infection with H7N1 in red-legged partridges seems to appear slightly later than in the H5N1 infected chicken and Chukar partridges . This delay in the onset of mortality could be due to the unique virulence of the H5N1 HPAIV . Clinically, progressive neurologic dysfunction, the most pronounced sign in surviving birds, correlated with the observations of Perkins and Swayne  in Chukar partridges. Gross lesions were observed in tissues that are known to be target organs for influenza A viruses in other gallinaceous species [8, 9], such as the kidney or fasciae sheaths of the muscles. The general predilection of the virus for epithelia of the upper digestive, respiratory and urinary tract, pancreas and liver, feather pulp and CNS, has been extensively described in chickens infected with other HPAIV subtypes [8, 23, 24]. Localisation of H7N1 antigen in the parenchyma of other organs, such as the lower digestive tract, bursa of Fabricius and skeletal muscle, was less consistent and more focalised, supporting the opinion that virus distribution in the host organism is dependent on particular host factors .
The onset of clinical signs in H7N1 birds, both intranasally inoculated and contact animals, proved effective transmission of the virus from infected partridges to naïve contact birds. Moreover, not only inoculated birds seroconverted but also contact birds. Surprisingly, at 1 dpi all inoculated animals only showed oropharyngeal shedding, suggesting that contact birds had been infected by virus shed from the oral cavity of the inoculated animals. This finding could indicate a shift from the classical faecal-oral route to the oral-oral route (possibly through shared drinking water) in H7N1 infection, as some authors have already pointed out [2, 9, 25, 26]. Our results suggest that in red-legged partridge, feather follicles could be a potential source for virus transmission, especially in recently dead individuals that are susceptible of feather picking. Interestingly, to date, few studies have evidenced the relevance of feathers as an important location for viral replication and potential origin of dissemination in HPAIV infection [27–29], and none of them have demonstrated the significance of this location in partridges.
The high susceptibility of partridges to H7N1 infection would make them a good sentinel species for detection of HPAIV. Since the partridges shed virus at high concentrations before death, this species could contribute to viral transmission during a local outbreak in free-living birds, in countries where partridges are found in the wild or are reared in outdoor operations. The delay between the onset of virus shedding and the appearance of clinical signs (around three days in the present experiment) could have important consequences in relation to the risk of spreading disease into the wild by releasing apparently healthy farm-reared partridges for hunting purposes. The implementation of sanitary surveillance measures prior to and after release is of importance to avoid introduction of avian influenza viruses, as well as other pathogens, in the natural ecosystem.
Our findings in H7N9 LPAIV infected birds correlate well with those obtained by Humberd et al.  in their experiment, in which no clinical disease was observed in ring-necked pheasants (Phasianus colchicus) and Chukar partridges infected with different subtypes of LPAIV. By this author, Chukar partridges were considered as short-term shedders of LPAIV, with the respiratory tract being the main viral excretion route. Likewise, in our study only limited viral shedding was detected in few inoculated birds most of which also seroconverted. Thus, our results suggest that partridges do not play a significant role as reservoir species for LPAIV, because only little, likely local, replication and short term shedding of low amounts of virus occurs in this species.
Based on our studies, firstly feather pulp, but also cloacal and oropharyngeal swabs, can be successfully used for virus detection in surveillance programs. In addition, the CNS and also pancreas and heart specimens are useful both for virus detection and histopathological diagnosis. In conclusion, although further studies with HPAIV and LPAIV strains should be performed, our observations suggest that the red-legged partridge is not likely to be a reservoir species for LPAI viruses but they are highly susceptible to H7N1 HPAIV and develop severe clinical disease and prolonged viral shedding. Thus, this species should be included in passive surveillance programs in order to prevent economical losses from HPAIV outbreaks.